Such devices and assemblies that make it possible to protect the needle by moving an inner sheath inside a support sheath are known.
Document FR 2 801 795 describes an assembly in which the inner sheath can be deployed automatically by drive means (in that example, by resilient means) so as to take up an active protection position around the needle at the end of the injection. However, the first time the inner sheath comes into contact with the skin of the patient can be somewhat unexpected and can surprise the patient, in particular since the contact takes place dynamically. Thereafter, a slight pressure, due to the drive exerted by the resilient means on the inner sheath until it is fully extracted from the support sheath, can be felt by the patient, until the needle is fully withdrawn from the flesh of the patient. However, that pressure is static and therefore there is no risk of causing the patient to suffer bruising.
In that type of device, the resilient means are generally rated to limit the magnitude of the contact pressure, by causing the inner sheath to slide gently out of the support sheath so that it does not slam against the skin of the patient. Thus, the contact against the skin of the patient takes place with gentleness that varies depending on the speed with which the inner sheath is driven out the support sheath, and, in general, depending on the magnitude of the drive exerted by the resilient means on the inner sheath.
However, the impact of the inner sheath against the skin can be unpleasant for the patient who is generally already worried by the injection.